It is known that dyes used in multicolor photographic elements do not transmit all of the electromagnetic radiation desired by theoretical photographic considerations. For example, the cyan dye, which should absorb radiation in the red region and transmit radiation in the green and blue regions of the electromagnetic spectrum, usually absorbs a small amount of radiation in the latter regions as well. The magenta and yellow dyes commonly used also exhibit undesirable absorptions. The result of printing a multicolor image formed with such dyes is to introduce undesirable amounts of color image regardless of the printing process parameters and sensitivity of the element. Color correction is therefore desirable and is generally accomplished with masking in some manner.
U.S. Pat. No. 2,449,966 (issued Sept. 21, 1968 to W. T. Hanson, Jr.) and the art mentioned therein describe various means for color correction of multicolor photographic elements, including the use of preformed dyes. Research Disclosure, publication 17643, paragraph VII, December 1978 and references described therein also describe color masking dyes. (Research Disclosure is available from Kenneth Mason Publications, Ltd., The Old Harbourmaster's, 8 North Street, Emsworth, Hampshire P010 7DD, United Kingdom). However, the compounds commonly used for color correction are already colored at the time of imagewise exposure. If such dyes and silver halide are incorporated in the same layer of a multicolor photographic element, the dye will act as an unwanted filter, absorbing a portion of the incident radiation which otherwise would reach silver halide in underlying layers. This results in a loss of sensitivity (i.e. photographic speed). One way to reduce this problem is to put masking dyes in only one layer of the multicolor elements, which generally have three color-forming layers. This solution is not desirable if masking is needed in the other layers. Another way to eliminate the unwanted filtering effect is to have the silver halide and the dye in separate layers while maintaining them in reactive association. While this is a useful and practical solution, it increases the number of layers in the element, making it thicker and presenting manufacturing and imaging inefficiencies.
U.S. Ser. No. 688,479 of W. N. Washburn, noted above, describes color masking dyes generated from ballasted colorless couplers containing a coupling-off group which will generate a color masking dye upon complexation with metal ions, e.g. ferrous ions. Although polymeric compounds of this invention are broadly within the description of the Washburn application, the focus of the Washburn application and its examples is on nonpolymeric ligand-releasing compounds. Although those compounds and the process of using them represent a significant advance in the art, the nonpolymeric ligand-releasing compounds described therein are difficult to disperse in aqueous coating compositions, and therefore require the use of coupler solvents to accomplish dispersion and coating. However, coupler solvents reduce the rate of metallization (i.e. complexation with metal ions) of the nonpolymeric colorless ligand-releasing compounds in unexposed areas of the element. Hence, in the time generally acceptable for processing of photographic elements, less dye may be formed. To overcome this deficiency, the elements can be subjected to an additional metal ion bath treatment to increase the dye formation sufficiently.
Therefore, it would be highly desirable to have a means for dye formation (e.g. color correction) in photographic elements which would allow easy formulation of coating compositions and avoid coupler solvents and the problems associated with them.